New research suggests this dysfunction in the brain's reward pathway
interferes with how people experience reward and motivation. Dopamine is a
chemical in the brain essential to normal functioning of the nervous
system.

"These deficits in the brain's reward system may help explain clinical
symptoms of ADHD, including inattention and reduced motivation, as well as the
propensity for complications such as drug abuse and obesity among ADHD
patients," says researcher Nora Volkow, MD director of the National Institute
on Drug Abuse, in a news release.

ADHD is a childhood psychological disorder that may also persist into
adulthood and affects 3%-5% of American adults.

Researchers say the results offer new insight into ADHD as well as help
explain why people with ADHD may be more likely to abuse drugs or become
obese.

The study, published in TheJournal of the American Medical
Association, used positron emission tomography (PET) brain scans to measure
markers of the brain's dopamine system in 53 non-medicated adults with ADHD and
a comparison group of 44 healthy adults.

The results showed that compared to the healthy adults, those with ADHD had
a reduction of dopamine receptors and transporters in two regions of the brain
involved in processing reward and motivation.

"This pathway plays a key role in reinforcement, motivation, and in learning
how to associate various stimuli with rewards," says Volkow. "Its involvement
in ADHD supports the use of interventions to enhance the appeal and relevance
of school and work tasks to improve performance."

"Our results also support the continued use of stimulant medications -- the
most common pharmacological treatment for ADHD -- which have been shown to
increase attention to cognitive tasks by elevating brain dopamine," Volkow
says.